Double wall bearing cup

ABSTRACT

A needle bearing cup includes an inner bearing cup having an inner surface which forms a rolling element raceway and an outer bearing cup disposed about the periphery of the inner bearing cup having a length greater than a length of the inner bearing cup to form a lip. The lip of the outer bearing cup is then formed to retain rolling elements within the inner bearing cup. Preferably, the rolling elements are needle rollers and the inner bearing cup is secured to an outer bearing cup by mechanical lock in the form of a protruding portion extending from the outer bearing cup. The bearing cup may be double drawn with first and second sheet metal blanks forming the inner and outer bearing cups. The lip of the outer bearing cup may be formed through ductile expansion using a punch having an inner diameter portion joined to an outer diameter portion with a step that contacts a top portion of the continuous sidewall portion of the inner bearing cup such that the lip extends about the outer diameter portion of the punch.

This ia a division of of Ser. No. 09/126,290 filed Jul. 30, 1998, nowU.S. Pat No. 6,419,398

BACKGROUND OF THE INVENTION

The invention relates generally to needle bearing cups, and moreparticularly to double drawn needle bearing cups having a shell formedfrom an outer cup and an inner cup.

FIG. 1 (PRIOR ART) is a cross sectional view of a conventional drawnneedle bearing cup. Conventional needle bearing cup 10 includes acylindrical shell 12 which is drawn from a piece of flat stock. Innersurface 14 of needle bearing cup 10 forms a bearing raceway for aplurality of rolling elements (not shown). The top portion of needlebearing cup 10 has a thinner cross section and is conventionallyreferred to as a lip 16. Needle bearing cup 10 houses a number ofinternal components such as the aforementioned rolling elements.Additional internal components may include a retainer cage to hold andguide the rolling elements, one or more seals, and less commonly,washers or rings for more specialized purposes.

FIG. 2 (PRIOR ART) illustrates conventional needle bearing cup 10 havinga number of internal components 18 installed within cylindrical shell12. Lip 16 is then bent over during final assembly to retain theinternal components. In order for lip 16 to be formed and maintain therequired ductility during final assembly, lip 16 is not heat treated tothe same extent as required for bearing raceway surface 14. Thus, aspecial heat treat process is required which prevents lip 16 from beingfully hardened when bearing cup 10 is heat treated. In the alternative,an additional temper or anneal process is required to soften lip 16prior to forming in the bent over position during final assembly.

The foregoing illustrates limitations known to exist in present devicesand methods. Thus, it is apparent that it would be advantageous toprovide an alternative directed to overcoming one or more of thelimitations set forth above. Accordingly, a suitable alternative isprovided including features more fully disclosed hereinafter.

SUMMARY OF THE INVENTION

In one aspect of the invention, this is accomplished by providing abearing cup including an inner bearing cup having an inner surface whichforms a bearing raceway. The inner bearing cup has a correspondinglength. An outer bearing cup is disposed about and continuous with theperiphery of the inner bearing cup and has a corresponding length whichis longer than the length of the inner bearing cup to form a lip. Thelip of the outer bearing cup may be formed to retain rolling elementswithin the bearing cup.

In another aspect of the invention, the limitations of the prior art areovercome by providing a method of forming a bearing cup having an innerbearing cup and an outer bearing cup. The method includes cutting firstand second sheet metal sections into first and second sheet metalblanks. The first and second sheet metal blanks are then drawn to form adouble walled bearing cup including an inner bearing cup correspondingto the first sheet metal blank and an outer bearing cup corresponding tothe second sheet metal blank. A lip is formed from the outer bearing cupand extends beyond a top portion of the inner bearing cup. Rollerelements are then installed within the inner bearing cup and the lip isbent over to retain the rolling elements within the inner bearing cup.

The foregoing and other aspects will become apparent from the followingdetailed description of the invention when considered in conjunctionwith the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 (PRIOR ART) is a cross sectional view of a conventional drawnneedle bearing cup;

FIG. 2 (PRIOR ART) is a cross sectional view of a conventional needlebearing cup having a lip bent over during final assembly to retaininternal components;

FIG. 3 a sectional view of a partially finished needle bearing cupformed from an inner bearing cup and an outer bearing cup according toan embodiment of the present invention;

FIG. 4 is a sectional view of a partially finished needle bearing cuppositioned over a punch having a smaller diameter portion and a largerdiameter portion according to an embodiment of the present invention;

FIG. 5 is a sectional view of a punch preventing an inner bearing cupfrom becoming elongated while an outer bearing cup is extended accordingto an embodiment of the present invention;

FIGS. 6 and 6A are sectional views of a needle bearing cup including aprotruding portion according to an embodiment of the present invention;and

FIG. 7 is a flow chart of the formation of a double drawn needle bearingcup according to an embodiment of the present invention.

DETAILED DESCRIPTION

Referring now to the drawings, FIG. 3 illustrates a sectional view of abearing cup 20 including an inner bearing cup 22 that may be formedwithin an outer bearing cup 24. Outer bearing cup 24 has a lip 26 whichextends beyond an upper wall of inner bearing cup 22. Preferably, outerbearing cup 24 is made from a material that remains relatively softduring a heat treat process which is required to harden inner bearingcup 22. Examples of materials that could be used include a high carbonsteel for inner bearing cup 22 and a low carbon steel for outer bearingcup 24.

According to an embodiment of the present invention, inner bearing cup22 and outer bearing cup 24 are formed simultaneously using a deepdrawing process. The deep drawing process is a double drawn process suchthat inner bearing cup 22 and outer bearing cup 24 are simultaneouslyformed from overlapping blanks of sheet metal. However, according toanother embodiment of the present invention, needle bearing cup 20 maybe manufactured by separately forming inner bearing cup 22 from a firstsheet metal blank and outer bearing cup 24 from a second sheet metalblank.

The advantages of separate material for inner bearing cup 22 and outerbearing cup 24 become apparent from the manufacturing process used toform needle bearing cup 20. A typical drawn cup manufacturing process isperformed in several steps, normally referred to as stations. Theoverall thickness of the material being drawn is directly related to thenumber of stations required to form the bearing cup. A substantiallythicker material requires additional stations to form a bearing cup thandoes a thinner material. A bearing cup including two cup layers may beformed more readily than a bearing cup having a single cup layer ofequal thickness. When two thinner bearing cups are double drawntogether, the two bearing cups act as though they are being formedindependently of the other and therefore can be made using fewerstations than would be required for a bearing cup having a single cuplayer.

As illustrated in FIG. 3, inner bearing cup 22 includes a bottom portion22 a and a continuous sidewall portion 22 b extending upwardlytherefrom. Likewise, outer bearing cup 24 includes a bottom portion 24 aand a continuous sidewall portion 24 b extending upwardly therefrom.Sidewall portion 22 b forms the bearing raceway and is generallycircular. As illustrated in FIG. 3, top portion 22 c of inner bearingcup 22 is substantially lower than top portion 24 c of outer bearing cup24 to expose lip 26.

A further advantage of drawing an inner cup and an outer cup together isthat lip 26 is formed from material of outer cup 26. During at least oneof the stations required to form a drawn bearing cup, the wall sectionis thinned, or “ironed” into a final size. The ironing station isprovided with a cylindrical die cooperating with a punch which forms theinside of the cup.

During the ironing process, the volume of material removed from innercup 22 or outer cup 24 is used to increase the length of the respectivecup. According to an embodiment of the present invention, a punch usedin the ironing process has two diameters, namely a smaller lowerdiameter which forms a rolling element raceway area, and a larger upperdiameter which forms lip 26. The point where the smaller diameter meetsthe larger diameter forms a step.

FIGS. 4 and 5 are sectional views of needle bearing cup 20 positionedover a punch 28 having a smaller diameter portion 30 and a largerdiameter portion 32 according to an embodiment of the present invention.Punch 28 has a step 34 which is formed at a point where smaller diameterportion 30 meets larger diameter portion 32. Prior to the ironing stepeffected by punch 28, inner bearing cup 22 is preferably formed of apredetermined length L₂₂ and outer bearing cup 24 is preferably formedof a predetermined length L₂₄. The length L₂₂ and length L₂₄ are formedsuch that top portion 22 c of inner bearing cup 22 is substantially thesame as top portion 24 c of outer bearing cup 24, and respectivelycorrespond to the lengths of sidewall portion 22 b and sidewall portion24 b.

With the proper selection of initial material thickness, needle bearingcup 20 is formed in one or more of the stations prior to the ironingstation such that the length of inner cup 22 is the same or slightlyshorter than a required length of the raceway in the final form. Thestep 34 in punch 28 is therefore the same or slightly longer than thelength of the cup coming into the ironing station.

As illustrated in FIG. 5, when cup 20 is ironed, the step 34 in punch 28prevents inner cup 22 from becoming further elongated. Therefore, mostof the excess volume of material from the ironing operation is producedfrom ductile extension of outer cup 24, which thereby forms lip 26. Theamount of ironing shown in FIG. 4 and FIG. 5 is exaggerated for clarity.

The process of forming lip 26 using material from outer cup 24 can beaided by selecting material for inner cup 22 which is significantlystronger, i.e. having a higher yield strength, than the material forouter cup 24. An example of materials which provide a significantdifference in strength for inner cup 22 and outer cup 24 is high and lowcarbon steel. Typical low carbon steels in a condition for drawingoperations have yield strengths in the range of 40,000 psi. High carbonsteels conditioned for drawing operations have yield strengths in therange of 60,000 psi. Since the outer material is weaker, the outermaterial will plastically yield first. Moreover, the majority of ironingoccurs in the outer material, and thus the material used to form lip 26comes from the outer material.

The above process of forming lip 26 also results in the length of innercup 22 not growing significantly during the ironing operation since itswall is not being thinned. If the material for outer cup 24 issignificantly ductile over and above inner cup 22, the length of innercup 22 will not significantly increase even if the step 34 of punch 28does not directly contact the top of inner cup 22. In this case, thedistance from step 34 of punch 28 to inner cup 22 may be sufficientlylong such that in the ironing station, material from outer cup 24 formsa protruding section above the end of inner cup 22.

FIGS. 6 and 6A are sectional views illustrating needle bearing cup 20 inwhich a protruding portion 36 from outer cup 24 extends above topportion 22 c of inner cup 22 according to an embodiment of the presentinvention. Protruding portion 36 provides a mechanical lock with innercup 22 which aids in physically holding the two cups together duringfurther processing and use.

The double wall cup design also allows the use of two entirely differentmaterials to create a bi-metallic structure. Typical drawn cup needlebearings are retained in their applications by a housing material withan interference fit. Problems can occur when the housing material has anhigher coefficient of thermal expansion than the cup material. In thiscase, as operating temperatures elevate, the differential growth betweenthe cup material and the housing material can result in a loss ofinterference fit. Furthermore, it is common for the housing material tobe of insufficient strength to act as the raceway surface. A typicalexample would be a ferrous cup material used in an aluminum housing.

Thus, a bi-metallic structure according to the present invention has anadvantage in that a double wall cup may be formed with a thinner innercup made from material suitable for application as a raceway and anouter cup made from a material which expands at elevated temperatures inclose relation to the housing material. According to this embodiment ofthe present invention, at elevated temperatures, the interference fitbetween the outer cup and the housing is maintained. Additionaladvantages may be obtained by using a stainless steel material for theouter cup to prevent the exposed area of the cup from corrosion.

FIG. 7 is a flow chart illustrating a method of forming a double drawnneedle bearing cup according to an embodiment of the present invention.As set forth in step 100, first and second sections of sheet metal arecut into shaped blanks. According to a preferred embodiment of thepresent invention, the first and second sheet metal blanks haveidentical shapes and are simultaneously formed. To form drawn needle cupbearings, the first and second sheet metal blanks are preferably in aform having an arcuate outer perimeter. More preferably, the first andsecond sheet metal blanks have a circular outer perimeter.

In step 101, the first and second blanks are formed into a double walledcup including inner cup 22 corresponding to the first blank and outercup 24 corresponding to the second blank. Step 101 may take severalstations to form the double walled cup. Inner bearing cup 22 and outerbearing cup 24 are preferably in a form illustrated in FIG. 4. In step101, the length of inner bearing cup 22 and the length of outer bearingcup 24 are preferably set to predetermined amounts. Preferably, thelength of inner bearing cup 22 is substantially equal to the length ofouter bearing cup 24.

In step 102, the bearing cups are formed with punch 28 having the step34. The step 34 of punch 28 contacts the top 22 c of inner bearing cup22 to prevent further elongation. The inner surface of inner bearing cup22 will become the rolling element raceway. On the other hand, step 34of punch 28 does not contact top portion 24 c of outer bearing cup 24,such that lip 26 is formed through ductile extension.

In step 103, internal components such as rolling elements are installedwithin the inner bearing cup 22. According to an embodiment of thepresent invention, the rolling elements are needle rollers. The internalcomponents may also include a retainer cage to hold and guide therolling elements, or one or more washers or rings for more specializedpurposes. In step 104, the lip 26 is bent over to retain the internalcomponents and complete the forming of needle bearing cup 20.

Having described the invention, what is claimed is:
 1. A bearing cupcomprising: an inner bearing cup having an inner surface which forms arolling element raceway, said inner bearing cup having a correspondinglength; and an outer bearing cup disposed about and continuous with theperiphery of said inner bearing cup, said outer bearing cup having acorresponding length which is longer than the length of said innerbearing cup to form a lip, whereby the lip of said outer bearing cup maybe formed to retain rolling elements within the bearing cup; said innerbearing cup being formed of a material that has a hardness greater thanmaterial forming said outer bearing cup.
 2. The bearing cup according toclaim 1 wherein the bearing cup is a needle bearing cup and the rollingelements are needle rollers.
 3. The bearing cup according to claim 1wherein said outer bearing cup has a protruding portion which provides amechanical lock with a top portion of said inner bearing cup.
 4. Thebearing cup according to claim 1 wherein said inner bearing cup isformed from a first metal and said outer bearing cup is formed from asecond metal different from said first metal such that the bearing cupis bi-metallic.
 5. The bearing cup according to claim 1 wherein saidinner bearing cup is formed of a high carbon steel and said outerbearing cup is formed of a lower carbon steel.
 6. The bearing cupaccording to claim 1 wherein each of said inner bearing cup and saidouter bearing cup comprises: a bottom portion; and a continuous sidewallportion extending from said bottom portion, the sidewall portion of saidouter bearing cup being thinner than the sidewall portion of said innerbearing cup.
 7. The bearing cup according to claim 1 wherein each ofsaid inner bearing cup and said outer bearing cup comprises: a bottomportion; and a continuous sidewall portion extending from said bottomportion, the lip of said outer bearing cup being formed through ductileextension of the outer bearing cup about a punch.
 8. The bearing cupaccording to claim 7 wherein, said punch has an inner diameter portionjoined to an outer diameter portion with a step and during formation ofthe lip, the inner diameter portion of the punch is received within thecontinuous sidewall portion of said inner bearing cup and the stepcontacts a top portion of the continuous sidewall portion of said innerbearing cup such that the lip extends about the outer diameter portionof the punch.
 9. The bearing cup according to claim 1 wherein said innerbearing cup and said outer bearing cup are double drawn.
 10. A bearingcup adapted for positioning in a housing formed from a material having afirst coefficient of thermal expansion, the bearing cup comprising: aninner bearing cup having an inner surface which forms a rolling elementraceway, said inner bearing cup having a corresponding length; and anouter bearing cup disposed about and continuous with the periphery ofsaid inner bearing cup, said outer bearing cup having a correspondinglength which is longer than the length of said inner bearing cup to forma lip, whereby the lip of said outer bearing cup may be formed to retainrolling elements within the bearing cup; said outer bearing cup beingformed of a material having a second coefficient of thermal expansionand the inner cup being formed of a material having a third coefficientof thermal expansion, the difference between the first and secondcoefficients of thermal expansion being less than the difference betweenthe first and third coefficients of thermal expansion and wherein saidinner bearing cup is formed of a high carbon steel and said outerbearing cup is formed of a lower carbon steel.
 11. The bearing cupaccording to claim 10 wherein the bearing cup is a needle bearing cupand the rolling elements are needle rollers.
 12. The bearing cupaccording to claim 10 wherein said outer bearing cup has a protrudingportion which provides a mechanical lock with a top portion of saidinner bearing cup.
 13. The bearing cup according to claim 10 whereinsaid inner bearing cup is formed from a first metal and said outerbearing cup is formed from a second metal different from said firstmetal such that the bearing cup is bi-metallic.
 14. The bearing cupaccording to claim 10 wherein each of said inner bearing cup and saidouter bearing cup comprises: a bottom portion; and a continuous sidewallportion extending from said bottom portion, the lip of said outerbearing cup being formed through ductile extension of the outer bearingcup about a punch.
 15. The bearing cup according to claim 14 whereinsaid punch has an inner diameter portion joined to an outer diameterportion with a step and during formation of the lip, the inner diameterportion of the punch is received within the continuous sidewall portionof said inner bearing cup and the step contacts a top portion of thecontinuous sidewall portion of said inner bearing cup such that the lipextends about the outer diameter portion of the punch.
 16. The bearingcup according to claim 10 wherein said inner bearing cup and said outerbearing cup are double drawn.
 17. A bearing cup adapted for positioningin a housing formed from a material having a first coefficient ofthermal expansion, the bearing cup comprising: an inner bearing cuphaving an inner surface which forms a rolling element raceway, saidinner bearing cup having a corresponding length; and an outer bearingcup disposed about and continuous with the periphery of said innerbearing cup, said outer bearing cup having a corresponding length whichis longer than the length of said inner bearing cup to form a lip,whereby the lip of said outer bearing cup may be formed to retainrolling elements within the bearing cup; said outer bearing cup beingformed of a material having a second coefficient of thermal expansionand the inner cup being formed of a material having a third coefficientof thermal expansion, the difference between to first and secondcoefficients of thermal expansion being less than the difference betweenthe first and third coefficients of thermal expansion and wherein eachof said inner bearing cup and said outer bearing cup comprises: a bottomportion; and a continuous sidewall portion extending from said bottomportion, the sidewall portion of said outer bearing cup being thinnerthan the sidewall portion of said inner bearing cup.